The effect of vertically sheared winds on fire plumes (i.e., buoyant plumes arising from intense heat sources based on or near the surface) is examined via numerical simulations of a compressible, nonhydrostatic model. In particular, the generation and evolution of vortical structures associated with the interaction of the plume with the sheared winds are investigated for a range of the controlling parameters [i.e., intensity of heat source, and magnitude of the shear]. Two types of plume are considered: (i) initially two-dimensional plumes associated with linear heat sources; and (ii) three-dimensional plumes associated with axisymmetric heat sources.

Plumes due to linear heat sources in the presence of a crossflow are shown to be unstable to transverse perturbations, such that a periodic array of vortices of alternating sign forms in the along-line direction. This instability apparently leads to a transition of the plume from its initial two-dimensional structure to a three-dimensional structure, particularly in the region far from the heat source. Plumes due to axisymmetric heat sources are dominated by an embedded counter-rotating vortex pair, which typically results in the bifurcation of the plume above the heat source. The development of these vortical features in the two types of plume is examined through the numerical simulations, as is the dependence of this development on the heat source intensity and crossflow shear.